A secondary additional objective is to collect exploratory information on potential predictors of prescription opioid self-administration including genetic polymorphisms, neurocognitive functioning, and response to stress. Blood samples will be collected to measure various genetic markers hypothesized to contribute to opioid drug effects (e.g., OPRM1, OPRD1, OPRK1, PENK, PDYN, DRD2, CYP3A4, and CYP2D6 genes). Performance on neurocognitive tasks and physiological response to the Trier Social Stress Test will be assessed in all participants.